The present invention relates generally to bridge construction techniques and more particularly to a method for building the deck structure of a cable-stayed girder bridge. The invention is particularly intended for utilization with the type of construction technique which involves formation of the deck girder section of a bridge in sequential stages with adjacent sections of the deck girder being successively formed. In the type of construction technique to which the present invention relates, a form carrier which is movable along the bridge during its formation is utilized. As each successive bridge section is formed, the form carrier is moved to extend in a cantilevered arrangement from a previously formed bridge section in order to thereby provide support for a successive bridge section during its formation.
The successively formed deck girder of the bridge consists of reinforced or prestressed concrete. With the formation of each segment of the deck girder, anchoring of the bridge support cables is effected and the anchored cables are tensioned prior to formation of a next section.
In bridges constructed from reinforced or prestressed concrete, it has been known to build the bridge superstructure in the form of two projecting arms which extend from a pier toward opposite sides and which consist of concrete cast in situ or of precast concrete units. The production occurs in successive cantilevered segments from a form carrier which is secured on a completed section of the bridge superstructure and which projects beyond the end thereof. Such a form carrier is moved on rollers along the bridge superstructure to enable formation of the next respective cantilever segment.
In the construction of bridge superstructures in a cantilever form of construction, a problem arises during the construction stage of the bridge with regard to adaption, to the fullest extent possible, of the static principle system of the unfinished bridge to the static system of the finished bridge. Only in this way can there be avoided problems such as the receipt by individual members of loads which are higher during the construction stage of the bridge than when the bridge is in its finished state. Also, in this manner, there may be avoided additional measures which might be required to absorb loads which occur only during the relatively short period of bridge construction, which measures might include the provision of additional reinforcements, auxiliary supports or the like.
A cable-stayed girder bridge usually consists of a deck girder which is carried by abutments and piers and additionally by a system of straight cables which extend obliquely from the approaches by way of one or more pylons to the main span or spans. The cables extend generally in vertical planes, either in a plane within the longitudinal axis of the bridge or on either side along the edges of the deck's girder. As the loads of a cable-stayed girder bridge are supported essentially by oblique cables, the deck girder does not have a great deal of bending strength. For this reason, cantilevering of a cable-stayed girder bridge, though possible in principle, presents difficulties because, due to the low bending strength of the deck girder, the pouring loads of the respective front cantilevered sections can be shifted back only to the previously produced section so that this section and the cable anchored therein are under greater load than in the final state of the bridge.
The present invention is aimed at overcoming many of the aforementioned problems. With utilization of the present invention, there may be obtained in the building of a cable-stayed girder bridge formed in successive cantilever sections, a better adaptation of the static principle system in the building stage of the bridge relative to the final system of the finished bridge whereby making possible a more economic production method for such a bridge.
Briefly, the present invention may be described as a process for the construction of a cable-stayed girder bridge which has a concrete deck girder including longitudinally extending stiffening girders and a laterally extending deck. The process is performed by sequential formation of the deck girder in successive adjacent sections utilizing a form carrier movable along the bridge and adapted to be cantilevered from a previously formed deck girder section to provide support for a successive deck girder section during its formation. The bridge of the type to which the present invention relates is supported from pylons anchored in the earth. Cables extend from the pylons to the longitudinal stiffening girders of the deck girder. The particular improvement of the present invention involves formation of the deck girder by first forming the longitudinal stiffening girders with the cables embedded therein. The longitudinal stiffening girders are permitted to set and harden and the cables embedded therein are subsequently tensioned between pylons and the formed stiffening girders. As a result, the cables may be utilized to provide additional support for the partially formed deck girder. During the pouring of the stiffening girders, the form carrier is arranged to extend in cantilever fashion from a previously formed deck girder. After formation of the stiffening girders, the form carrier is connected to the formed stiffening girders to thereby enable additional support to be provided for the section being constructed. Finally, the laterally extending deck portion of the deck girder may be formed and this stage of the construction of the bridge may be effected with the advantage that the cables enhance the support which would otherwise be provided only by the form carrier.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described a preferred embodiment of the invention.